Industrial waste water results from the use of water as a cooling medium and also from the use of water in numerous wet-working processes, for example the use of water as a solvent in chemical processes and for such other uses as washing, soaking, distilling, filtering, and rinsing, which may involve the cleaning of apparatus used in these processes. Impurities are present in this industrial waste water in the form of solid or liquid components of the waste water which may be dissolved or partially in colloidal form, etc. The industrial waste water treatment is dependent, at least in part, on whether the impurities are of inorganic or organic origin. Such treatment includes biological treatment, for example by utilizing microorganisms, and chemical/or physical treatments. Neutralization and flocculation methods are technically classified as chemical waste water purification treatments. Acid-containing waste waters are generally neutralized, for example with lime. Alkaline waste waters are generally neutralized, with for example hydrochloric acid or sulfuric acid. The solid material which is precipitated in conjunction with and/or as an adjunct to treatments involving neutralization, for example finely divided sludge in the form of floc can be removed in a mechanical clarification apparatus adjoining the chemical treatment. Coagulation processes for the separation of material in suspension and in colloidal solution which do not settle are utilized.
The solid material in the form of sludge or flocs, which is the end-product of such a water purification process, is removed from the water in a sedimentation plant. Two types of gravity separators are generally used for this purpose.
Settling basins for waste water plants are basins through which the water is passed. The rate of flow of the water is reduced to such an extent that solid material can settle in the form of bottom sludge. Specific lighter materials can flow to the surface. Settling basins are usually rectangular in shape. Large plants have automatic means for removing sludge, such as blade scrapers, chain scrapers, or reciprocating blade scrapers, which through their back-and-forth motion at the edge of the basin push the coagulated sludge into a pump sump from which it is drawn off and transported by pumps.
Conventional settling basins have the disadvantage of requiring a large amount of space. Generally, the water authorities require retention periods of four to six times the flow rate, for example, a 10 m.sup.3 /hr flow rate for a settling basin volume of 40-60 cubic meters. These basins have the advantage that there is no critical reaction with respect to changes in the sludge content and in the volume of water flowing through the basin.
Conventional waste water plants also utilize inclined separators which are also called plate separators or lamella separators. These separators correspond to a plurality of settling tanks which are stacked one upon the other and are in an inclined position. Utilizing this construction, the sedimentation surface is multiplied for a given volume of tank. Because of the inclined position of the surfaces, the sludge slides down into the collecting portion of the inclined separator. Such an apparatus permits a substantial reduction of the retention time in the separator (for example as little as a few minutes) and therefore a smaller space requirement for the equipment for treatment of a given volume of waste water. These inclined separators are very high because of the height requirements for the stack of inclined plates on top of the sludge collector. This large height requirement is a disadvantage. These inclined separators are also very sensitive and do not operate well when there is a large sludge mass which occurs in surges. Furthermore, because of the short retention time the sludge does not thicken sufficiently so that the sludge removed from the inclined separator has to be further treated in special thickeners. Therefore, in practice the advantage of lesser volume of separator is in the context of all the equipment, lost, especially when using smaller units such as up to 10 m.sup.3 /hr.
It is an object of the present invention to provide an efficient process and apparatus for clarification of waste water and removal of fine particles therefrom.